1. Field of Invention
The present invention relates to a display device for displaying letters, numbers, patterns, and the like. The present invention also relates to an electronic watch for measuring and displaying time, such as a wristwatch or a stopwatch.
2. Description of Related Art
Hitherto, a display device, which displays numbers, letters, and other types of information by utilizing a flat display such as a liquid crystal display, has been widely known. As such a display device, for example, a display device shown in FIG. 20 is well known, in which a pair of polarizers 52 and 53 are located on both sides of a liquid crystal panel 51 and a reflector 54 is located on the back side of one of the polarizers 53. The pair of polarizers 52 and 53 are placed, for example, so that their polarization axes form a right angle.
In this conventional display device, information, such as numbers, are displayed by applying a predetermined on-state voltage between electrodes of the liquid crystal panel 51, and a background of white or the like is displayed by not applying a voltage. In the figure, a region where an on-state voltage is applied is indicated by "ON", and a region where a voltage is not applied is indicated by "OFF".
In this display device, when a voltage is not applied to the liquid crystal panel 51, as shown by arrow P, linearly polarized light of the external light, that is, natural light that is polarized parallel to the plane of the page passes through the polarizer 52, and is turned into linearly polarized light polarized perpendicular to the plane of the page with its polarization direction twisted through an angle of 90.degree. by the liquid crystal panel 51 in the off state. After passing through the polarizer 53, this linearly polarized light is irregularly reflected by the surface of the reflector 54. A part of the irregularly reflected light sequentially passes through the polarizer 53, the liquid crystal panel 51, and the polarizer 52, and is visible to an outside viewer. This part is thereby perceived as a reflection image from the reflector 54, normally, as a uniform white background.
Next, when an on-state voltage is applied to the liquid crystal panel 51, as shown by arrow Q, linearly polarized light that is parallel to the plane of the page is separated from the external light by the polarizer 52, and passes through the liquid crystal panel 51. Since the liquid crystal panel 51 is in an on state at this time, the polarization direction of the linearly polarized light is kept parallel to the plane of the page without being twisted, and therefore, this linearly polarized light is absorbed by the polarizer 53. As a result, this part is perceived as a dark color, such as black, from outside.
As mentioned above, in this conventional display device, information, such as numbers, is displayed in a dark color of black or the like on a reflection image from the reflector 54, normally, on a uniform white background.
Furthermore, for example, Japanese Unexamined Patent Publication No. 52-55565 discloses the technique of forming the reflector 54, which constitutes a display section of an electronic watch, of a solar battery. According to this electronic watch, a power supply for watch driving is charged with an electromotive force of the solar battery, and the liquid crystal panel and the like are driven by the charged watch-driving power supply.
As mentioned above, while it has been already known that the reflector 54 in the display device is formed of a solar battery, since the surface of the solar battery usually has a dark color, such as black or dark blue, when a background is displayed by reflecting external light by the reflector 54, as shown by arrow P in FIG. 20, it is displayed in a dark color of black or the like. On the other hand, information, such as numbers, is displayed in a dark color of black or the like by using a light absorption property of the polarizer 53, as shown by the arrow Q.
In short, when the reflector is formed of a solar battery in the conventional display device, information, such as numbers, is displayed in a dark color of black or the like on a background of a similar dark color such as black. Therefore, the information, such as numbers, cannot be clearly distinguished. Consequently, the technique of placing a solar battery within a display plane of a watch or the like has not yet been put into actual use. When the solar battery is used, it cannot help being located outside the display plane of the watch or the like.